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•H E A D S - U P : E X A M # 1 F R I D A Y , S E P T E M B E R
1 8 TH
How many C atoms are in a 0.96-carat diamond
ring? (1 carat = 0.2g)
1. 9.63 x 1021
25%
25%
25%
2
3
25%
2. 1.38 x 1024
3. 4.81 x 1022
4. 3.47 x 1025
1
20
4
Compounds and Moles
 1 mole of a compound contains 6.022 x 1023
molecules or “units”
 Molar mass = sum of atomic molar masses



H2O
CO2
Fe(NO3)3
Examples to try
(answers posted on web site under lecture notes)
Consider UF6
•
•
•
•
•
What is the molar mass?
How many grams in 0.5 mol?
How many molecules in 0.5 mol?
How many U atoms in 0.5 mol of UF6?
How many F atoms in 0.5 mol UF6?
Molecular vs. Nonmolecular compound terms
 1 mol CO2 contains 6.022 x 1023 molecules
 1 mol NaCl contains 6.022 x 1023 formula units
Percent Composition
 The fraction of mass due to an element




mass
of
eleme
#
atom
of
elem
in
for
ma
of
el
Percent
compos
n

x
100
%

x
1
%
total
mass
mas
of
com
Determining Formulas from % Composition
 The ratio of atoms in the formula is the same as the
ratio of moles of those elements.
 If you determine the ratio of moles, you know the
formula.
 However, the formula determined is the empirical
formula.
Which of the following has the highest %
composition of copper, Cu? (don’t calculate)
1. CuSO4
25%
25%
25%
2
3
25%
2. Cu2SO4
3. CuCO3
4. Cu2CO3
1
4
Examples
1. 8.65g of iron combines with 3.72g of oxygen.
What is the empirical formula of this
compound?
2. Formaldehyde contains 40.0% C, 6.7% H, and
53.3% O. What is the empirical formula?
Empirical vs. Molecular Formulas
 Formaldehyde
 Empirical= CH2O


Molar mass of empirical
formula= 30.03g/mol
Actual Molar mass=
30.03g/mol
 Fructose
 Empirical= CH2O




Molecular= CH2O
Molar mass of empirical
formula= 30.03g/mol
Actual Molar mass=
180.16g/mol
Divide actual molar mass
by empirical formula mass
to get multiplier:
180.16/30.03=6

Molecular= C6H12O6
Example
A hydrocarbon has 82.65%C and 17.34%H. The
molar mass is 58.12 g/mol. What are the
empirical and molecular formulas?